Coding mode signaling for small blocks

ABSTRACT

An apparatus for video encoding includes processing circuitry that determines that a current block is not coded in an intra block copy (IBC) mode. Responsive to the determination that the current block is not coded in the IBC mode, the processing circuitry determines whether a size of the current block is greater than a threshold. The processing circuitry encodes a mode prediction flag into a coded bitstream based on the size of the current block being greater than the threshold. The mode prediction flag indicates whether the current block is coded in an intra prediction mode.

INCORPORATION BY REFERENCE

This present application is a continuation of U.S. patent applicationSer. No. 16/822,780, “CODING MODE SIGNALING FOR SMALL BLOCKS,” filed onMar. 18, 2020, which claims the benefit of priority to U.S. ProvisionalApplication No. 62/821,241, “CODING MODE SIGNALING FOR SMALL BLOCKS”filed on Mar. 20, 2019. The disclosures of the prior applications areincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs of aneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described herein is atechnique henceforth referred to as “spatial merge.”

Referring to FIG. 1C, a current block (111) can include samples thathave been found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (112 through 116, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry.

According to aspects of the disclosure, there is provided a method forvideo decoding in a decoder. In the method, prediction information for acurrent block in a current picture that is a part of a coded videosequence is decoded. A determination is made as to whether the currentblock is coded in an intra block copy (IBC) mode based on the predictioninformation. Responsive to the current block not being coded in the IBCmode, a determination is made as to whether a size of the current blockis above a threshold. The current block is determined to be coded in anintra prediction mode based on a determination that the size of thecurrent block is not above the threshold. The current block isreconstructed based on the intra prediction mode.

In an embodiment, the threshold comprises a 4×4 luma sample size.

According to aspects of the disclosure, the prediction informationcomprises a group type and an IBC flag indicating whether the IBC isenabled for the current block. The group type comprises a slice type, atile type, or a tile group type.

In an embodiment, the current block is determined to be coded in theintra prediction mode based on the determination that the size of thecurrent block is above the threshold and a determination that theprediction information indicates the tile type included in the grouptype is an I (intra) type for the current block.

In an embodiment, responsive to the current block not being coded in theIBC mode, a prediction mode of the current block is determined based ona prediction mode flag when included in the prediction information.

According to aspects of the disclosure, the prediction informationcomprises a sequence parameter set (SPS) IBC enabled flag that indicateswhether the IBC mode is enabled in the SPS.

In an embodiment, responsive to the prediction information indicatingthat the tile type included in the group type for the current block isan I-type (intra type) and the IBC flag for the current block is notincluded, whether the current block is coded in the IBC mode isdetermined based on the SPS IBC enabled flag.

In an embodiment, responsive to the prediction information indicatingthat the tile type included in the group type for the current block is anon-I type and the IBC flag for the current block is not included, thecurrent block is determined not to be coded in the IBC mode.

Aspects of the disclosure provide an apparatus configured to perform anyone or a combination of the methods for video decoding. In anembodiment, the apparatus includes processing circuitry that decodesprediction information for a current block in a current picture that isa part of a coded video sequence. The processing circuitry determineswhether the current block is coded in an intra block copy (IBC) modebased on the prediction information. Responsive to the current block notbeing coded in the IBC mode, the processing circuitry determines whethera size of the current block is above a threshold. The processingcircuitry determines that the current block is coded in an intraprediction mode based on a determination that the size of the currentblock is not above the threshold. The processing circuitry reconstructsthe current block based on the intra prediction mode.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform any one or acombination of the methods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions;

FIG. 1C is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example;

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment;

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment;

FIG. 6 is a block diagram of an encoder in accordance with anotherembodiment;

FIG. 7 is a block diagram of a decoder in accordance with anotherembodiment;

FIG. 8A is an illustration of exemplary intra prediction directions andcorresponding intra prediction modes in some examples (e.g., VVC);

FIG. 8B is an example of intra block copy (IBC) prediction mode inaccordance with an embodiment of the disclosure;

FIG. 9A is an exemplary syntax table in accordance with an embodiment;

FIG. 9B is another exemplary syntax table in accordance with anembodiment;

FIG. 9C illustrates an inter prediction mode table in accordance with anembodiment;

FIG. 10 shows a flow chart outlining an exemplary process in accordancewith an embodiment of the disclosure; and

FIG. 11 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector allowed reference area,and so forth. The controller (550) can be configured to have othersuitable functions that pertain to the video encoder (503) optimized fora certain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (603), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Inter Prediction in VVC

Beyond the inter coding features in HEVC, a number of new and refinedinter prediction coding tools are included in VVC, such as extendedmerge prediction, merge mode with MVD (MMVD), affine motion compensatedprediction, subblock-based temporal motion vector prediction (SbTMVP),triangle partition prediction, and combined inter and intra prediction(CIIP).

For each inter-predicted coding unit (CU) in VVC, motion parametersinclude motion vectors, reference picture indices and reference picturelist usage index, and additional information needed for new codingfeatures of VVC to be used for inter-predicted sample generation. Themotion parameters can be signaled in an explicit or implicit manner.When a CU is coded with skip mode, the CU can be associated with one PUand have no significant residual coefficients, e.g., no coded motionvector delta or reference picture index. A merge mode can be specifiedwhereby the motion parameters for the current CU are obtained fromneighboring CUs, including spatial and temporal candidates, andadditional merge modes introduced in VVC, such as affine merge, mergewith motion vector difference (MMVD), combined inter and intraprediction (CIIP), etc. The merge mode can also be applied, in additionto the inter-predicted CUs in skip mode, to other inter-predicted CUs.An alternative to the merge mode is explicit transmission of motionparameters, where the motion vectors, the corresponding referencepicture index for each reference picture list, reference picture listusage flag, and other needed information are signaled explicitly pereach CU.

III. Intra Prediction in VVC

FIG. 8A shows an illustration of exemplary intra prediction directionsand corresponding intra prediction modes in some examples (e.g., VVC).In FIG. 8A, there are a total of 95 intra prediction modes (modes−14˜80), among which mode 0 is planar mode (referred to asINTRA_PLANAR), mode 1 is DC mode (referred to as INTRA_DC), and othermodes (modes −14˜−1 and modes 2˜80) are angular (or directional) modes(also referred to as INTRA_ANGULAR). Among the angular (or directional)modes, mode 18 (referred to as INTRA_ANGULAR18) is a horizontal mode,mode 50 (referred to as INTRA_ANGULAR50) is a vertical mode, and mode 2(referred to as INTRA_ANGULAR2) is a diagonal mode that points to abottom-left direction, mode 34 (referred to as INTRA_ANGULAR34) is adiagonal mode that points to a top-left direction, and mode 66 (referredto as INTRA_ANGULAR66) is a diagonal mode that points to a top-rightdirection. Modes −14˜−1 and Modes 67˜80 are referred to as wide-angleintra prediction (WAIP) modes.

IV. Intra Block Copy (IBC) Prediction in VVC

Current picture referencing (CPR) is sometimes referred to as intrablock copy (IBC), where a motion vector refers to already reconstructedreference samples in a current picture. CPR was supported in HEVC screencontent coding extension (HEVC SCC) for example. A CPR-coded CU issignaled as an inter-coded block. A luma motion (or block) vector of theCPR-coded CU is in integer precision. A chroma motion vector of theCPR-coded CU is clipped to integer precision. When combined with AMVR(Advanced MVP), the CPR mode can switch between 1-pel and 4-pel motionvector precisions. The current picture is placed at the end of thereference picture list L0. To reduce memory consumption and decodercomplexity, the CPR can allow only the reconstructed portion of thecurrent CTU to be used. This restriction allows, for example, the CPRmode to be implemented using local on-chip memory for hardwareimplementations.

At an encoder side, hash-based motion estimation can be performed forCPR. The encoder performs a rate distortion (RD) check for blocks witheither width or height no larger than, for example, 16 luma samples. Fornon-merge mode, the block vector search is performed using a hash-basedsearch first. If the hash-based search does not return a validcandidate, a block matching based local search will be performed.

In the hash-based search, a hash key matching (e.g., 32-bit CRC) betweenthe current block and a reference block is extended to all allowed blocksizes. The hash key calculation for each position in the current pictureis based on, for example, 4×4 sub-blocks. For the current block of alarger size, a hash key is determined to match the hash key of thereference block when all the hash keys of all 4×4 sub-blocks match thehash keys in the corresponding reference locations. If hash keys ofmultiple reference blocks are found to match the hash key of the currentblock, the block vector costs of each matched reference are calculatedand the one with the minimum cost is selected.

In the block matching based local search, a search range is set to be Nsamples to the left and on top of the current block within the currentCTU. At the beginning of the block matching based local search, thevalue of N is initialized to, for example, 128, if there is no temporalreference picture. The value of N is initialized to, for example, 64, ifthere is at least one temporal reference picture. A hash hit ratio isdefined as the percentage of samples in the CTU that found a match usingthe hash-based search. While encoding the current CTU, if the hash hitratio is below, for example, 5%, N is reduced, for example, by half.

FIG. 8B shows an example of the IBC prediction mode, according to anembodiment of the disclosure. In the example of FIG. 8, a currentpicture (800) is being reconstructed and includes a reconstructed area(801) (gray area) and a to-be-decoded area (802) (white area). Theblocks in the reconstructed area (801) are already decoded and theblocks in the to-be-reconstructed area (802) are either being decoded orto-be-decoded. A current block (804) is in the to-be-reconstructed area(802) and being decoded. The current block (804) can be decoded from areference block (805) that is in the reconstructed area (801). Thedecoding of the current block (804) is based on a block vector (803)that is an offset between the current block (804) and the referenceblock (805).

V. Block Size Based Constraint for Inter Prediction

In some related examples, a block size based constraint is applied oninter prediction. For example, inter prediction is disabled for blocksof certain sizes (e.g., 4×4 luma samples), and/or inter bi-prediction isdisabled (inter uni-prediction is allowed) for blocks of certain sizes(e.g., 8×4 or 4×8 luma samples).

VI. Coding Mode Signaling for Small Blocks

The disclosure includes embodiments to optimize the block size basedconstraint for inter prediction by optimizing coding mode signaling forsmall blocks.

The present methods (or embodiments) may be used separately or combinedin any order. Further, each of the methods (or embodiments) andapparatuses (e.g., various encoders and decoders) may be implemented byprocessing circuitry (e.g., one or more processors or one or moreintegrated circuits). In one example, the one or more processors executea program that is stored in a non-transitory computer-readable medium.In the disclosure, the term block may be interpreted as a predictionblock, a coding block, or a coding unit, i.e. CU.

When the inter prediction is disabled for blocks with size being lessthan or equal to a size threshold, the signaling methods present in thedisclosure may be used. In the present methods (or embodiments), thesize threshold can be set to be 4×4 luma samples. If the size thresholdis set to another size, such as a size larger than 4×4 luma samples, thecondition of “equal to 4” or “equal to 4×4” can be changed to “less thanor equal to” the actual size threshold.

FIG. 9A shows an exemplary syntax table in accordance with anembodiment, in which inter prediction is disabled for 4×4 blocks. In theFIG. 9A example, the array indices x0, y0 specify the location (x0, y0)of the top-left luma sample of the current coding unit relative to thetop-left luma sample of the current coding picture. The variablescbWidth and cbHeight indicate a block width and a block height of thecurrent coding unit, respectively. The variable treeType indicates acoding tree type of the current coding unit.

The variables tile_group_type and sps_ibc_enabled_flag indicate a tilegroup type and a sequence parameter set (SPS) IBC flag for the currentcoding unit, respectively. The variable tile_group_type can be either aI type for intra prediction type or a non-I type for non-intraprediction type (e.g., P or B type). The variable sps_ibc_enabled_flagcan be equal to 1 (or true) when IBC prediction mode is enabled in theSPS, or be equal to 0 (or false) when IBC prediction mode is disabled inthe SPS.

In addition, when the variable cu_skip_flag is equal to 0 (or false),the current coding unit is not coded in skip mode. When the variablecu_skip_flag is equal to 1 (or true), the current coding unit can becoded in skip mode.

When the variable pred_mode_flag is equal to 0 (or false), the currentcoding unit can be coded in inter prediction mode. When the variablepred_mode_flag is equal to 1 (or true), the current coding unit can becoded in intra prediction mode.

The variable CuPredMode[x][y] can be derived as follows for x=x0 . . .x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1. If the variablepred_mode_flag is equal to 0, CuPredMode[x][y] can be set equal toMODE_INTER. Otherwise (e.g., when the variable pred_mode_flag is equalto 1), CuPredMode[x][y] can be set equal to MODE_INTRA.

When the variable pred_mode_flag is not present (or signaled), thevariable pred_mode_flag can be inferred to be equal to 1 when an I tilegroup is being decoded or when a coding unit with size of 4×4 lumasamples is being decoded, and can be inferred to be equal to 0 when a Por B tile group is being decoded, respectively.

When the variable pred_mode_ibc_flag is equal to 1 (or true), thecurrent coding unit can be coded in IBC prediction mode. When thevariable pred_mode_ibc_flag is equal to 0 (or false), the current codingunit is not coded in IBC prediction mode.

When the variable pred_mode_ibc_flag is not present (or signaled), thepred_mode_ibc_flag can be inferred to be equal to the value of thevariable sps_ibc_enabled_flag when an I tile group is being decoded orwhen a coding unit coded in skip mode and with size of 4×4 luma samplesis being decoded, and can be inferred to be equal to 0 when a P or Btile group is being decoded, respectively.

When the variable pred_mode_ibc_flag is equal to 1, the variableCuPredMode[x][y] can be set to be equal to MODE_IBC for x=x0 . . .x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1.

In one embodiment, the variable pred_mode_flag can be signaled beforethe variable pred_mode_ibc_flag. When the current blocks size is 4×4luma samples, the prediction mode of the current coding unit is notequal to MODE_INTRA (e.g., CuPredMode[x0][y0]!=MODE_INTRA), and the CUskip flag is true (e.g., cu_skip_flag[x0][y0]==1), the variablepred_mode_ibc_flag is not signaled but can be inferred to be equal totrue.

The method of FIG. 9A can be further improved and optimized according toaspects of the disclosure, such as using the method of FIG. 9B, whichshows another exemplary syntax table in accordance with an embodiment.In the FIG. 9B example, all the variables (e.g., x0, y0, cbWidth,cbHeight, treeType, tile_group_type, sps_ibc_enabled flag,CuPredMode[x][y], cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag,etc.) can have the same meaning with those of the FIG. 9A example,except as described below.

In the FIG. 9B example, when the variable pred_mode_ibc_flag is notpresent (or signaled), the variable pred_mode_ibc_flag can be inferredto be equal to the value of sps_ibc_enabled_flag when an I tile group isbeing decoded, and can be inferred to be equal to 0 (false) when a P orB tile group is being decoded, respectively.

When the variable pred_mode_ibc_flag is equal to 1 (or true), thevariable CuPredMode[x][y] can be set to be equal to MODE_IBC for x=x0 .. . x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1.

When the variable pred_mode_ibc_flag is equal to 0 (false), the variableCuPredMode[x][y] can be derived as follows for x=x0 . . . x0+cbWidth−1and y=y0 . . . y0+cbHeight−1. If the variable pred_mode_flag is equal to0, CuPredMode[x][y] can be set to be equal to MODE_INTER. Otherwise(e.g., when the variable pred_mode_flag is equal to 1), CuPredMode[x][y]can be set to be equal to MODE_INTRA.

When the variable pred_mode_flag is not present (or signaled) and thevariable pred_mode_ibc_flag is 0, the variable pred_mode_flag can beinferred to be equal to 1 when an I tile group is being decoded or whena coding unit with size of 4×4 luma samples is being decoded, and can beinferred to be equal to 0 when a P or B tile group is being decoded,respectively.

In one embodiment, the variable pred_mode_ibc_flag is signaled beforethe variable pred_mode_flag. When the current blocks size is equal to4×4 luma samples and the variable pred_mode_ibc_flag is not equal to 1(or true), the variable pred_mode_flag is not signaled but can beinferred to be equal to 1.

FIG. 9C shows a table of exemplary inter prediction modes in accordancewith an embodiment. In FIG. 9C, inter_pred_idc[x0][y0] specifies whetherlist0 (PRED_L0), list1 (PRED_L1), or bi-prediction (PRED_B1) is used forthe current coding unit according to the table. The array indices x0, y0specify the location (x0, y0) of the top-left luma sample of theconsidered coding block relative to the top-left luma sample of thepicture. When inter_pred_idc[x0][y0] is not present (or signaled), itcan be inferred to be equal to list0 (PRED_L0).

VII. Flow Chart

FIG. 10 shows a flow chart outlining an exemplary process (1000)according to an embodiment of the disclosure. In various embodiments,the process (1000) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (1000) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1000).

The process (1000) may generally start at step (S1010), where theprocess (1000) decodes prediction information for a current block in acurrent picture that is a part of a coded video sequence. Then theprocess (1000) proceeds to step (S1020).

At step (S1020), the process (1000) determines whether the current blockis coded in an intra block copy (IBC) mode based on the predictioninformation. Responsive to the current block not being coded in the IBCmode, the process (1000) proceeds to step (S1030). Responsive to thecurrent block being coded in the IBC mode, the process (1000) proceedsto step (S1060).

In an embodiment, the prediction information comprises an IBC flag thatindicates whether the current block is coded in the IBC mode.

In an embodiment, the prediction information comprises a group type thatcomprises a slice type, a tile type, or a tile group type.

At step (S1030), the process (1000) determines whether a size of thecurrent block is above a threshold. Responsive to the size of thecurrent block not being above the threshold, the process (1000) proceedsto step (S1040). Responsive to the size of the current block being abovethe threshold, the process (1000) proceeds to step (S1070).

At step (S1040), the process (1000) determines that the current block iscoded in an intra prediction mode. Then the process (1000) proceeds tostep (S1050).

At step (S1050), the process (1000) reconstructs the current block basedon the intra prediction mode.

At step (S1060), the process (1000) reconstructs the current block basedon the IBC mode.

At step (S1070), the process (1000) determines whether the tile typeincluded in the group type is an I (intra) type. Responsive to the tiletype included in the group type being the I (intra) type, the process(1000) proceeds to step (S1040). Otherwise, the process (1000) proceedsto step (S1080).

At step (S1080), the process (1000) reconstructs the current block basedon a prediction mode flag when included in the prediction information.

After reconstructing the current block, the process (1000) terminates.

In an embodiment, the threshold comprises a 4×4 luma sample size.

According to aspects of the disclosure, the prediction informationcomprises an SPS IBC enabled flag for the current block that indicateswhether the IBC mode is enabled in the SPS.

In an embodiment, the process (1000) determines that the current blockis coded in the intra prediction mode based on the determination thatthe size of the current block is above the threshold and a determinationthat the prediction information indicates the tile type included in thegroup type is an I (intra) type for the current block.

In an embodiment, responsive to the current block not being coded in theIBC mode, the process (1000) determines a prediction mode of the currentblock based on a prediction mode flag when included in the predictioninformation.

In an embodiment, responsive to the prediction information indicatingthat the tile type included in the group type for the current block isthe I-type (intra type) and the IBC flag for the current block is notincluded, the process (1000) determines whether the current block iscoded in the IBC mode based on the SPS IBC enabled flag.

In an embodiment, responsive to the prediction information indicatingthat the tile type included in the group type for the current block is anon-I type and the IBC flag for the current block is not included, theprocess (1000) determines the current block is not coded in the IBCmode.

VIII. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 11 shows a computersystem (1100) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 11 for computer system (1100) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1100).

Computer system (1100) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1101), mouse (1102), trackpad (1103), touchscreen (1110), data-glove (not shown), joystick (1105), microphone(1106), scanner (1107), camera (1108).

Computer system (1100) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1110), data-glove (not shown), or joystick (1105), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1109), headphones(not depicted)), visual output devices (such as screens (1110) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted). These visual output devices (such as screens(1110)) can be connected to a system bus (1148) through a graphicsadapter (1150).

Computer system (1100) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1120) with CD/DVD or the like media (1121), thumb-drive (1122),removable hard drive or solid state drive (1123), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1100) can also include a network interface (1154) toone or more communication networks (1155). The one or more communicationnetworks (1155) can for example be wireless, wireline, optical. The oneor more communication networks (1155) can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of the one or more communication networks (1155) includelocal area networks such as Ethernet, wireless LANs, cellular networksto include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (1149) (such as, for example USB ports of thecomputer system (1100)); others are commonly integrated into the core ofthe computer system (1100) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1100) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1140) of thecomputer system (1100).

The core (1140) can include one or more Central Processing Units (CPU)(1141), Graphics Processing Units (GPU) (1142), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1143), hardware accelerators for certain tasks (1144), and so forth.These devices, along with Read-only memory (ROM) (1145), Random-accessmemory (1146), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1147), may be connectedthrough the system bus (1148). In some computer systems, the system bus(1148) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1148),or through a peripheral bus (1149). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1141), GPUs (1142), FPGAs (1143), and accelerators (1144) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1145) or RAM (1146). Transitional data can be also be stored in RAM(1146), whereas permanent data can be stored for example, in theinternal mass storage (1147). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1141), GPU (1142), massstorage (1147), ROM (1145), RAM (1146), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1100), and specifically the core (1140) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1140) that are of non-transitorynature, such as core-internal mass storage (1147) or ROM (1145). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1140). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1140) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1146) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1144)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

Appendix A: Acronyms

-   AMVP: Advanced Motion Vector Prediction-   ASIC: Application-Specific Integrated Circuit-   ATMVP: Alternative/Advanced Temporal Motion Vector Prediction-   BDOF: Bi-directional Optical Flow-   BIO: Bi-directional Optical Flow-   BMS: Benchmark Set-   BV: Block Vector-   CANBus: Controller Area Network Bus-   CB: Coding Block-   CBF: Coded Block Flag-   CCLM: Cross-Component Linear Mode/Model-   CD: Compact Disc-   CPR: Current Picture Referencing-   CPUs: Central Processing Units-   CRT: Cathode Ray Tube-   CTBs: Coding Tree Blocks-   CTUs: Coding Tree Units-   CU: Coding Unit-   DPB: Decoder Picture Buffer-   DVD: Digital Video Disc-   FPGA: Field Programmable Gate Areas-   GOPs: Groups of Pictures-   GPUs: Graphics Processing Units-   GSM: Global System for Mobile communications-   HDR: High Dynamic Range-   HEVC: High Efficiency Video Coding-   HRD: Hypothetical Reference Decoder-   IBC: Intra Block Copy-   IC: Integrated Circuit-   ISP: Intra Sub-Partitions-   JEM: Joint Exploration Model-   JVET: Joint Video Exploration Team-   LAN: Local Area Network-   LCD: Liquid-Crystal Display-   LTE: Long-Term Evolution-   MPM: Most Probable Mode-   MTS: Multiple Transform Selection-   MV: Motion Vector-   OLED: Organic Light-Emitting Diode-   PBs: Prediction Blocks-   PCI: Peripheral Component Interconnect-   PDPC: Position Dependent Prediction Combination-   PLD: Programmable Logic Device-   PU: Prediction Unit-   RAM: Random Access Memory-   ROM: Read-Only Memory-   SBT: Sub-block Transform-   SCC: Screen Content Coding-   SDR: Standard Dynamic Range-   SEI: Supplementary Enhancement Information-   SNR: Signal Noise Ratio-   SSD: Solid-state Drive-   TUs: Transform Units-   USB: Universal Serial Bus-   VPDU: Visual Process Data Unit-   VUI: Video Usability Information-   VVC: Versatile Video Coding-   WAIP: Wide-Angle Intra Prediction

What is claimed is:
 1. A method for video encoding in an encoder,comprising: determining that a current block is not coded in an intrablock copy (IBC) mode; responsive to the determination that the currentblock is not coded in the IBC mode, determining whether a size of thecurrent block is greater than a threshold; and encoding a modeprediction flag into a coded bitstream based on the size of the currentblock being greater than the threshold, the mode prediction flagindicating whether the current block is coded in an intra predictionmode.
 2. The method of claim 1, wherein the encoding comprises: encodingthe mode prediction flag into the coded bitstream based on (i) the sizeof the current block being greater than the threshold and (ii) a grouptype of the current block not being an intra type.
 3. The method ofclaim 1, further comprising: determining that the current block is codedin the intra prediction mode based on at least one of (i) the size ofthe current block not being greater than the threshold or (ii) a grouptype of current block being an intra type.
 4. The method of claim 2,wherein the group type includes one of a slice type, a tile type, or atile group type.
 5. The method of claim 1, wherein the determining thatthe current block is not coded in the IBC mode comprises: determiningthat the current block is not coded in the IBC mode based on at leastone of a first IBC flag or a second IBC flag, the first IBC flagindicating whether the current block is coded in the IBC mode, and thesecond IBC flag indicating whether the IBC mode is enabled in a sequenceparameter set (SPS).
 6. The method of claim 5, wherein the determiningthat the current block is not coded in the IBC mode comprises:responsive to a group type of the current block being an intra type andthe first IBC flag of the current block not being encoded, determiningthat the current block is not coded in the IBC mode based on the secondIBC flag indicating that the IBC mode is not enabled in the SPS.
 7. Themethod of claim 5, further comprising: encoding the first IBC flag intothe coded bitstream based on the second IBC flag indicating that the IBCmode is enabled in the SPS and at least one of (i) a group type of thecurrent block not being an intra type or (ii) the group type of thecurrent block being the intra type and the current block not being codedin a skip mode.
 8. The method of claim 1, wherein the thresholdcomprises a 4×4 luma sample size.
 9. An apparatus, comprising:processing circuitry configured to: determine that a current block isnot coded in an intra block copy (IBC) mode; responsive to thedetermination that the current block is not coded in the IBC mode,determine whether a size of the current block is greater than athreshold; and encode a mode prediction flag into a coded bitstreambased on the size of the current block being greater than the threshold,the mode prediction flag indicating whether the current block is codedin an intra prediction mode.
 10. The apparatus of claim 1, wherein theprocessing circuitry is configured to: encode the mode prediction flaginto the coded bitstream based on (i) the size of the current blockbeing greater than the threshold and (ii) a group type of the currentblock not being an intra type.
 11. The apparatus of claim 1, wherein theprocessing circuitry is configured to: determine that the current blockis coded in the intra prediction mode based on at least one of (i) thesize of the current block not being greater than the threshold or (ii) agroup type of current block being an intra type.
 12. The apparatus ofclaim 10, wherein the group type includes one of a slice type, a tiletype, or a tile group type.
 13. The apparatus of claim 9, wherein theprocessing circuitry is configured to: determine that the current blockis not coded in the IBC mode based on at least one of a first IBC flagor a second IBC flag, the first IBC flag indicating whether the currentblock is coded in the IBC mode, and the second IBC flag indicatingwhether the IBC mode is enabled in a sequence parameter set (SPS). 14.The apparatus of claim 13, wherein the processing circuitry isconfigured to: responsive to a group type of the current block being anintra type and the first IBC flag of the current block not beingencoded, determine that the current block is not coded in the IBC modebased on the second IBC flag indicating that the IBC mode is not enabledin the SPS.
 15. The apparatus of claim 13, wherein the processingcircuitry is configured to: encode the first IBC flag into the codedbitstream based on the second IBC flag indicating that the IBC mode isenabled in the SPS and at least one of (i) a group type of the currentblock not being an intra type or (ii) the group type of the currentblock being the intra type and the current block not being coded in askip mode.
 16. The apparatus of claim 9, wherein the threshold comprisesa 4×4 luma sample size.
 17. A non-transitory computer-readable storagemedium storing a program executable by at least one processor toperform: determining that a current block is not coded in an intra blockcopy (IBC) mode; responsive to the determination that the current blockis not coded in the IBC mode, determining whether a size of the currentblock is greater than a threshold; and encoding a mode prediction flaginto a coded bitstream based on the size of the current block beinggreater than the threshold, the mode prediction flag indicating whetherthe current block is coded in an intra prediction mode.
 18. Thenon-transitory computer-readable storage medium of claim 17, wherein thestored program further causes the at least one processor to perform:encoding the mode prediction flag into the coded bitstream based on (i)the size of the current block being greater than the threshold and (ii)a group type of the current block not being an intra type.
 19. Thenon-transitory computer-readable storage medium of claim 17, wherein thestored program further causes the at least one processor to perform:determining that the current block is coded in the intra prediction modebased on at least one of (i) the size of the current block not beinggreater than the threshold or (ii) a group type of current block beingan intra type.
 20. The non-transitory computer-readable storage mediumof claim 18, wherein the group type includes one of a slice type, a tiletype, or a tile group type.